1. Field of the Invention
The present invention relates to an automatic document feeder for conveying consecutively document sheets to an information reading position of an image forming apparatus for forming an image on a document sheet such as an electrophotographic copying machine for example, and more particularly to an automatic document feeder being capable of efficiently performing a both-faces processing operation.
2. Prior Art
An image forming apparatus such as an electrophotographic copying machine and the like as described above uses a sheet conveying device called an automatic document feeder (ADF) so as to automatically draw out and feed one by one a plurality of document sheets to a position where the content of a document is read. Recently, such an automatic document feeder is composed so as to be able to process not only a document sheet having information recorded on one face of it but also a document sheet having information on both faces of it.
As such an automatic document feeder capable of performing both one-face processing and both-faces processing operations, for example Japanese Patent Laid-Open Publication No. Hei 10-81,449 has disclosed a composition making it possible to efficiently perform both one-face processing and both-faces processing operations.
According to this publicly known technique, in the one-face processing mode, document sheets each having information on its upside which are stacked in order on a paper feed stacker are drawn out one by one from the top, and each of them is turned over in a paper feed path and is scanned at an information reading position and then is discharged as it is. At this time, since document sheets to be discharged onto a paper discharge stacker are stacked in order as their information faces are kept looking down, finally the document sheets discharged do not need to be rearranged and therefore, efficient operations can be performed.
And in the both-faces processing mode, document sheets each having the odd-number page as its upside which are stacked in order on the paper feed stacker are drawn out one by one from the top, and each of them is turned over in the paper feed path and is scanned at the information reading position and then is guided to a switchback path provided at the downstream side of the information reading position. A pair of switchback rollers are arranged in the switchback path, and a document sheet turned back by this pair of switchback rollers is guided again to the paper feed path, is turned over here and the back face of it is scanned at the information reading position and then is guided to the switchback path as it is. And it is made to switchback and is discharged in a turned-over state.
At this time, since document sheets to be discharged onto the paper discharge stacker are stacked in order as their odd-number pages are kept looking down, finally the document sheets discharged do not need to be rearranged and therefore, efficient operations can be performed. And since the passage of a document sheet at the information reading position is limited to the irreducible minimum, the damage of a document sheet is reduced and the time for processing a document sheet is shortened and therefore document sheets can be consecutively and efficiently processed.
According to an automatic document feeder composed as described above, in case of processing the back face of a document sheet in the both-faces processing mode, a document sheet turned back from the switchback path is conveyed again into the switchback path after the back face of it has been processed. At this time, since the fore end and the rear end of a document may overlap each other at the position of the pair of switchback rollers, the pair of switchback rollers are arranged distantly from the feed roller so as not to hinder the conveyance of a document sheet.
In such a way, however, only by arranging the pair of switchback rollers distantly from the feed roller, the switchback path has to be made longer in consideration of processing a large-sized document sheet and thereby the apparatus results in being made large-sized as a whole.
Further, a conventional apparatus cannot handle a long-sized document sheet longer than a specified size since it is jammed in the switchback path.
The present invention has been performed in consideration of the problems in the switchback path of the above-mentioned prior art, and an object of the present invention is to provide an automatic document feeder which has a switchback path and can perform a both-faces processing operation, said automatic document feeder capable of simplifying the control of a switchback operation and making it possible to handle a long-sized document sheet without making large the diameter of a feed roller and without making the switchback path unnecessarily long, and thereby making it possible to process a more long-sized document sheet as keeping the automatic document feeder small-sized as a whole.
In order to solve the above-mentioned problems, the present invention provides an automatic document feeder comprising a feed path for feeding a document sheet drawn out from a paper feed stacker to an image reading portion facing a feed roller, a switchback path for making a document sheet which has been processed at the image reading portion switchback, a pair of switchback rollers which are provided so as to make a document sheet switchback in the switchback path and are able to turn forward and backward, and a paper discharge path for discharging a document sheet being in said switchback path onto a paper discharge stacker, wherein said switchback path is provided in a casing below said paper discharge stacker and said casing has an opening formed in it so that the fore end of a document sheet guided into the switchback path projects from the casing.
Hereupon, said casing is provided with a guide member for covering a document sheet projecting from said opening from the upper side and guiding it downward below said opening.
As described above, in an automatic document feeder according to the present invention, since the fore end of a document sheet projects from an opening of a casing, the automatic document feeder of the invention can be made small-sized as coping with the maximum size of document sheets to be handled.
In the present invention, differently from such a composition providing an opening in a switchback path, a curved portion may be formed in said switchback path so as to curve a document sheet guided into the switchback path in said switchback path. Due to this, it is possible to prevent a long-sized document sheet from being jammed in the switchback path.
Further, the present invention provides an image reader comprising a conveying means for drawing out one by one document sheets stacked on a paper feed stacker, conveying a document sheet to an image reading portion to optically read a document and discharging a read document sheet onto a paper discharge stacker, wherein said conveying means is composed of a feed means for feeding said document sheet to the image reading portion facing a feed roller, a switchback means for making a document sheet which has been read at the image reading portion switchback, a pair of switchback rollers which are provided so as to make a document sheet switchback in a switchback path and are able to turn forward and backward, and a paper discharge means for discharging a document sheet being in said switchback path onto a paper discharge stacker, wherein said pair of switchback rollers are disposed at a position in the switchback path where the fore end and the rear end of a document sheet being the largest in size to be handled do not overlap each other through said feed roller when said document sheet is made to switchback and is fed again to said feed roller.
Hereupon, the switchback path is provided in a casing below said paper discharge stacker, and an opening is formed in said casing so that the fore end of a document sheet guided into the switchback path projects from the casing, and said casing is provided with a guide member for covering a document sheet projecting from said opening from the upper side and guiding it downward below said opening, or said switchback path has a curved portion formed so as to curve a document sheet guided into the switchback path in said switchback path.
Furthermore, the present invention controls said pair of switchback rollers to turn slower when guiding a document sheet into the switchback path than when discharging the document sheet from the switchback path in order to make it possible to control more accurately the switchback position of a document sheet when making the document sheet switchback in the switchback path.
Due to this, the present invention has realized an automatic document feeder and an image reader being more small-sized in which when a both-faces reading process of a document sheet is performed the ends of a document sheet made to switchback between a switchback path and a feed roller do not overlap each other at the position of the pair of switchback rollers and a long-sized document sheet is not jammed in the switchback path.